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All‐inorganic CsPbI3 perovskite semiconductor is attractive for deep‐red light‐emitting diodes (LEDs) because of its high photoluminescence, good thermal stability, excellent charge transport, and solution processability. However, the metastable phase of optically active CsPbI3 hinders the fabrication of efficient and bright deep‐red LEDs. Herein, a multifunctional ionic ligand regulation strategy using (2‐hydroxy‐5‐methylphenyl) triphenyl‐phosphonium iodide and 3‐(N, N‐dimethyloctylammonio) propanesulfonate is reported to regulate the optically active CsPbI3 crystallization and thus obtain high‐quality γ‐CsPbI3 thin films. The high crystallinity and preferential orientation of γ‐CsPbI3 arise from the strong bonding between the ionic ligands and ionic lead halide clusters. The obtained γ‐CsPbI3 thin films also possess suppressed defect densities, high luminescence, and high stability. Using this high‐quality thin film, an efficient and bright deep‐red LED with a peak external quantum efficiency of 13.34% and a maximum luminance of 2110 cd m−2 is successfully fabricated. The operational lifetime of the fabricated LED (time to half of the initial brightness, T50) reaches up to 40 min under a high current density of 50 mA cm−2 (corresponding to the initial brightness of 200 cd m−2). [ABSTRACT FROM AUTHOR]

Mixed halide perovskite nanocrystals show great promise for high-performance light-emitting diodes (LEDs) due to their tunable band gaps, high photoluminescence efficiency, and excellent color purity. However, one major challenge in using mixed halide CsPbBrxCl3–x NCs for pure blue LEDs is the instability of their electroluminescence (EL) caused by halide segregation. Here, we report an effective pseudohalide tetrafluoroborate (BF4–) passivation approach to improve the EL stability of CsPbBrxCl3–x NC-based LEDs. Our approach involves the solution-processed treatment of CsPbBrxCl3–x NCs by the complex of tributylphosphine oxide and calcium tetrafluoroborate, which yields pseudohalide BF4–-passivated CsPbBrxCl3–x NCs. The BF4– fills the surface halide ion vacancy, providing dual benefits of surface passivation and halide migration suppression. By using these BF4–-passivated CsPbBrxCl3–x NCs as the emitting layer, we have successfully fabricated spectrally stable and pure blue LEDs with an emission peak at 468 nm, a maximum luminance of 275 cd/m2, and a maximum external quantum efficiency of 3.2%. Our proposed BF4–-passivated NCs strategy will pave the way for the development of efficient, stable, and pure blue perovskite LEDs. [ABSTRACT FROM AUTHOR]

Solution-processed light-emitting diodes (LEDs) based on copper–iodide clusters are promising candidates for solid state lightings due to their abundance, environmental friendliness and high luminescent efficiency. However, the development of this class of LEDs is hampered by the instability of the clusters, poor solution compatibility and low film quality, resulting in poor device performances. Here we report a new type of copper–iodide cluster hybrids with functional groups that facilitate both solubility and stability of the clusters. The hybrid clusters exhibit high structural stability in solvents, enabling smooth solution-processed thin films with low surface roughness of 0.22 nm and high photoluminescence quantum yields of over 70%. We employ the high-quality thin film as an emissive layer in warm-white LEDs, showing a maximum external quantum efficiency of 19.1%, maximum high brightness of over 40,000 cd m−2 and a good operational lifetime of 232 h (T50 at an initial luminance of 100 cd m−2). We also demonstrate a large-area LED with brightnesses of up to ~60,000 cd m−2 through blade-coating and a series of colour-tunable LEDs based on ligand modifications. Our results suggest great potential of copper–iodide cluster-based LEDs for practical applications in panel display and solid-state lighting. Solution-processed copper–iodide clusters are employed as efficient emitters for warm white LEDs with external quantum efficiency of 19.1%. [ABSTRACT FROM AUTHOR]

Metal halide perovskite light‐emitting diodes (PeLEDs) are promising high‐definition display candidates due to their narrow emission bandwidth and wide color gamut. However, efficient and stable pure‐red PeLEDs have rarely been achieved. Herein, a robust and strongly‐coordinated sulfate anion passivation strategy is reported to achieve a spectrally stable and efficient pure‐red PeLED with an electroluminescent peak at 630 nm and full width at half maximum of 27 nm. Octylammonium sulfate is employed to construct a PbSO4 layer on the surface of CsPbI3−xBrx nanocrystals, which can effectively inhibit phase separation under UV light, humidity, or heat treatment. Using sulfate passivated CsPbI3−xBrx NC film, pure red PeLEDs with high external quantum efficiency of 12.6%, excellent spectral stability, and an operational half‐life time of over 300 min (T50@100 cd cm−2) are fabricated. This work provides a new avenue to improve performance of pure red PeLEDs via strong‐coordinated sulfate passivation. [ABSTRACT FROM AUTHOR]

Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor. [ABSTRACT FROM AUTHOR]

Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor. [ABSTRACT FROM AUTHOR]

Hierarchically structured chiral luminescent materials hold promise for achieving efficient circularly polarized luminescence. However, a feasible chemical route to fabricate hierarchically structured chiral luminescent polycrystals is still elusive because of their complex structures and complicated formation process. We here report a biomimetic non-classical crystallization (BNCC) strategy for preparing efficient hierarchically structured chiral luminescent polycrystals using well-designed highly luminescent homochiral copper(I)-iodide hybrid clusters as basic units for non-classical crystallization. By monitoring the crystallization process, we unravel the BNCC mechanism, which involves crystal nucleation, nanoparticles aggregation, oriented attachment, and mesoscopic transformation processes. We finally obtain the circularly polarized phosphors with both high luminescent efficiency of 32% and high luminescent dissymmetry factor of 1.5 × 10−2, achieving the demonstration of a circularly polarized phosphor converted light emitting diode with a polarization degree of 1.84% at room temperature. Our designed BNCC strategy provides a simple, reliable, and large-scale synthetic route for preparing bright circularly polarized phosphors. Chiral emitters with high photoluminescence quantum yield are desirable for use in circularly polarized LEDs. The authors demonstrate the transfer of chirality from nanoscale copper iodide clusters to microscale chiral luminescent polycrystals by non-classical crystallization. [ABSTRACT FROM AUTHOR]